In a conventional CMOS image sensor chip, photosensitive devices of pixels, such as photodiodes, are disposed within the same semiconductor layer together with MOS devices of in-pixel signal amplifier circuitries. This leads to a large overall area and hence low light reception efficiency of the pixels, as well as more difficulties in optimizing the photosensitive devices and the MOS devices of the signal amplifier circuitries.
Exmor sensors are developed by Sony Corporation by referencing the patent document U.S. Pat. No. 8,946,798 and employing a technique to form a three-dimensional stack of semiconductor chips through bonding the chips and interconnecting them using through silicon vias (TSV's). In the stack, the peripheral processing circuitries are partially separated from the photosensitive devices and arranged under the photosensitive devices while being connected to the photosensitive devices by the TSV's. This arrangement can effectively reduce the overall area of the chips and facilitate the design optimization and the fabrication process optimization of the MOS devices of the peripheral processing circuitries in the photosensitive devices.
However, with similarity to the conventional front- or backside-illuminated image sensors, in the Exmor sensors of the Sony Corporation, in-pixel amplifier circuitries are also disposed within the same semiconductor layer as photodiodes. Therefore, these photosensitive imaging apparatuses still suffer from the following perceived deficiencies:
1. The optical fill factor of a photodiode in a pixel is limited due to active MOS transistors disposed in the same pixel. Therefore, the footprint of the MOS transistors bottlenecks photoelectric efficiency enhancement and maintenance of the photosensitive imaging apparatus.
2. Incident and residual optical radiation entering a pixel is unfavorable for the performance of active MOS transistors and p-n junctions therein, for example, for their signal noise suppression.
3. Footprint of the photodiodes forms a limitation to layout optimization of the in-pixel amplifier circuitries and hence impedes overall performance enhancement of the photosensitive imaging apparatus.
4. The MOS devices of the in-pixel amplifier circuitries and photodiodes disposed within the same semiconductor layer restrict each other, making the design optimization and the fabrication process optimization of these different semiconductor devices difficult.